BACKGROUND: Patients who have been exposed to human tissue by prior transplants, blood transfusion or pregnancy may develop and maintain anti-bodies against these foreign human cells (SENSITIZATION). As a result of sensitization these patients are more likely to reject an organ donated from an individual who possesses a similar human cell marker (ANTIGENIC)profile. These sensitized patients will remain on the kidney transplant waiting list up to twice as long as those who are not pre-sensitized.